Method for controlling the suspension of a vehicle by processing images from at least one on-board camera

ABSTRACT

The disclosed method checks the state of degradation of the suspension of a vehicle without having to carry out tests that immobilize the vehicle or to use non-objective expertise. The method processes data provided by at least one front camera in an on-board visual system. The checking method includes steps for periodically acquiring images provided by the camera or cameras, followed by storage of the positional data of the three-dimensional road in relation to a flat road and basic positional parameter data for the path of the vehicle. The error between the ideal values of the suspension parameters of a chosen suspension model and the values of these parameters corresponding to the stored path data from the positional data is then minimized. By iteration, the accuracy ε of the error reaches a predetermined value sufficient to diagnose a state of the suspension.

The present invention relates to a method for checking the state ofdegradation of a suspension system fitted to a motor vehicle byprocessing image data provided by at least one on-board camera carriedby the vehicle, and in particular by two cameras in a stereoscopicsystem.

Motor vehicle suspension performs two functions: helping to keep thevehicle safely on the road under all circumstances (braking, cornering,different road surfaces, etc.) and ensuring comfortable conditions forpassengers in an insulated passenger compartment (noise, vibration,shocks, etc.).

These goals are generally at odds, and so require compromise solutions,in particular between the stiffness of the springs and the compressionratio of the shock absorbers generally making up the motor vehiclesuspension members on each wheel.

In order to monitor the state of a suspension system, with a view toestimating the appropriate time to change same by identifying a criticaldegree of degradation due to ageing of the components or faults thatworsen over time, the suspension may be tested manually during a roadworthiness test, although such solutions are dependent on the degree ofexpertise of the operative, or a test bench may be used to provideobjective results.

These benches test the effectiveness of the suspension by measuringadhesion values, in particular using the measurement method provided bythe European Shock Absorber Manufacturers Association (EUSAMA).

However, the measurements provided by such test benches are not preciseenough to determine the state of a suspension system in terms offull-scale behaviour in a real context.

The present invention is intended to check the state of degradation ofthe suspension of a vehicle safely and continuously without having tocarry out tests that immobilize the vehicle or to use non-objectiveexpertise. To do so, the invention proposes processing the data providedby at least one front camera in a visual system carried on board thevehicle.

Such cameras are generally designed for driver assistance units. Theseunits are used to detect obstacles located in the visual field in frontof these vehicles.

In particular, stereoscopic systems are able to precisely determine thedistance between the vehicle and the obstacles located in front of thevehicle using two on-board cameras arranged close to one another toprovide pairs of images to a digital processing unit. The distancebetween these obstacles and the vehicle is then detected by analyzingthe disparity between the images formed. The driver can thenadvantageously be made aware of the obstacles recognized by means of awarning signal in the driver assistance system.

Such cameras may also have other functions, such as detecting thecontinuous line and providing a warning if the continuous line iscrossed, automatically deactivating full-beam headlights when passing avehicle in the opposite direction (at least partial deactivation byswitching to dipped headlights or switching at least one headlight tostandby), detecting pedestrians and triggering emergency brake ifnecessary, etc.

According to the invention, data related to the presence ofirregularities on the road that are provided by processing images fromthe visual system, as well as data related to the position of thevehicle on said road, are used to check the state of the suspension ofthe vehicle in relation to a reference suspension.

More specifically, the present invention relates to a method forchecking the state of degradation of a suspension system fitted to amotor vehicle comprising the following steps:

-   -   periodic acquisition of successive images of a forward field of        vision provided by at least one camera in a visual system        carried on board the vehicle and stored in the form of pixels,    -   storage of positional data of a real three-dimensional road in        relation to a reference road considered to be flat, using the        pixels stored in the previous step,    -   storage of the basic rotational and translational positional        parameter data of a path of the vehicle using the positional        data memorized in relation to the flat road,    -   minimization of an error between the predetermined intrinsic        suspension parameter values of a suspension model in an ideal        state and the intrinsic suspension parameter values of said        model corresponding to the basic positional parameter data of        the path stored in the previous steps,    -   iteration of the previous step until an accuracy 6 of said error        reaches a predetermined value ε_(R) to diagnose a state of the        suspension as a function of the deviation determined during the        previous step, and    -   triggering of an alarm in the event of diagnosis of a        pre-critical suspension state.

In a preferred embodiment, the on-board visual system is a stereoscopicsystem comprising two cameras providing pairs of images in order toconstruct three-dimensional data on the basis of the disparities, whichare preferably digitally filtered, between each pair of images.

According to particularly advantageous embodiments:

-   -   the road considered to be flat is determined by averaging the        standard deviations of the data on the real three-dimensional        road with a predetermined number of pixels,    -   the path of the vehicle is identified by successive values of        specific parameters relating to the height of the        three-dimensional road and of the vehicle, and to the roll        rotation and/or pitch rolling of the vehicle, these specific        positional parameter values being determined using the stored        data for the real three-dimensional road and the basic        positional parameters,    -   the suspension model for each wheel of the vehicle is selected        from a library including a model single-stage suspension system        with equivalent springs or equivalent springs/shock absorbers        arranged in parallel, and a two-stage suspension system with        equivalent springs or equivalent springs/shock absorbers        assembled in parallel for a suspension stage proper, and with        equivalent springs or equivalent spring/shock absorbers arranged        in parallel for a tire stage,    -   the suspension parameters relate to the stiffness of the        equivalent spring or springs and the compression ratio of the        equivalent shock absorber or shock absorbers per wheel,    -   the suspension is controlled by active, semi-active or passive        control,    -   the accuracy ε of the suspension parameter values enables the        state of inflation of the tires to be determined,    -   the accuracy ε of the suspension parameter values makes it        possible to determine which of the suspension proper or the        tire(s) is in a pre-critical state.

Other data, characteristics and advantages of the present invention areset out in the detailed nonlimiting description below, provided withreference to the figures attached which show, respectively:

FIG. 1 is a transparent perspective view of a motor vehicle showing thesuspension members arranged on each wheel of the vehicle,

FIG. 2 is a side view of a vehicle schematically showing an examplesuspension model of the suspension members proper and of the tires ofthe vehicle,

FIG. 3 is a side view of the profiles of the real path of a camera inthe visual system carried on-board the vehicle, of the anticipated pathof this camera estimated using the suspension model, and of the road onwhich the vehicle is running, and

FIG. 4 is a logical diagram for implementing the method for checking thestate of the suspension of a vehicle according to the invention.

FIG. 1 is a transparent perspective view of a vehicle 1 showing thesuspension 10 of same. This suspension 10 comprises, respectively forthe front and rear wheels 2 a, 2 b, helical springs 3 a and 3 b mountedcoaxially with (on the front axle 10A in the example) or close to (onthe rear axle 10B in the example) the front and rear shock absorbers 4a, 4 b, these springs and shock absorbers forming the front and rearsuspension members proper 11A, 11B, and the tires 5 a and 5 b mounted onthe corresponding wheels 2 a and 2 b.

Such a suspension system 10 is active in the example shown, i.e.controlling this suspension enables the vehicle to be kept on a flatpath if the suspension is a perfect reference suspension system, thispath being held at a given height in relation to the ground while thevehicle is in movement.

Alternatively, suspension control is deemed to be semi-active when samedoes not oppose the vertical movement of the wheels, but compensates forthis movement to prevent same from being amplified. If no suspensioncontrol is used, this control is deemed to be passive, in the absence ofany control or standby state.

The vehicle 1 also includes cameras 6 and 7 in a stereoscopic system 60that are assembled on an on-board supporting element 12 arranged on theupper edge of the windshield 1 b of the vehicle 1.

In order to illustrate a suspension model 10, the side view of thevehicle body 1 c in FIG. 2 shows, in model form, the front and rearsuspension members proper 11A and 11B and the front and rear tires 5 a,5 b in FIG. 1.

Each of the suspension members proper 11A or 11B comprises an equivalentspring 3′a or 3′b and a shock absorber that are assembled in parallel,each shock absorber being represented by a piston 41 combined with anoil cylinder 42. A suspension control actuator 6A and 6B is provided foreach suspension member proper in order to adjust the suspension activelyfor each wheel 2 a and 2 b (FIG. 1).

Each suspension member proper 11A or 11B bears a sprung mass Msestimated to be one quarter of the mass of the vehicle body 1 c.Furthermore, each tire, represented here by a spring 5′a, 5′b, bears anunsprung mass Mu, estimated to be one quarter of the chassis. Thestiffness of the springs and the compression ratio of the shockabsorbers are set in advance to enable the actuators to distribute themasses optimally at all times when the vehicle is in movement.

Under these conditions, the pairs of images of the forward field ofvision Va successively stored by the stereoscopic system 60 rigidlyattached to the body 1 c also save the behaviour of the vehicle thatdepends on the state of the suspension of same.

This behaviour is entirely determined using variations in the six basicpositional parameters in an orthogonal reference system OXYZ, threerotations (pitch, roll and yaw, respectively about the axes OX, OY andOZ) and three translational movements (parallel to the axes OX, OY andOZ), as conventionally applied. In this case, the reference system OXYZis oriented according to the reference road 100 considered to be flat,which is determined by averaging the standard deviations of the pixelsof the road from the forward field of vision Va (i.e. of a realthree-dimensional road 110) successively stored. Fewer than six basicparameters may be used in simplified embodiments.

Determining successive values of the six basic parameters saved by thestereoscopic system makes it possible to determine, using a suitablematrix transformation, the variations in the values of the specificpositional parameters, defining the path of the vehicle 1 on thereference road 100 and characterizing the behaviour of the vehicle inrelation to the state of the suspension of same.

In the example, these specific positional parameters relate to thevariation in height “h” of the irregularities 101 in the realthree-dimensional road 110 in relation to the reference road 100, aswell as two other parameters related to the position of the vehicle inthe reference system OXYZ, specifically the height “z” of same measuredalong the axis OZ and the pitch rotation of same “⊖” about the axis OX.Alternatively, roll rotation of the vehicle may be added, or pitchrotation may be replaced by roll rotation.

The side view in the plane ZOY in FIG. 3 shows the path Ts of a camera 6in the stereoscopic system of the vehicle moving on a profile of a realthree-dimensional road 110, in which OY matches the linear profile ofthe reference road 100 mentioned above. The path Ts is determined usingthe saved images in relation to the reference road 100 and matches thepath of the vehicle body 1 c stabilized by the active suspensioncontrols 6A, 6B (FIG. 2).

FIG. 3 also shows the ideal path T0 of the camera 6 parallel to thereference road 100 when the suspension is considered to be ideal withthe suspension model in question (see FIG. 2). This ideal path T0 isparallel to the linear profile of the reference road 100: the deviationsΔz between the paths Ts and T0 therefore resulting from the variationsin the specific positional parameters “z” and “ε” of the vehicle due toworsening state of the suspension with reference to an ideal state inthe suspension model used (see FIG. 2).

The logical diagram in FIG. 4 shows implementation of the method forchecking the state of the suspension of a vehicle according to theinvention, using the previous example based on a stereoscopic systemcarried on-board a vehicle. For this purpose, the stereoscopic systemhas a digital module for processing the data coming from the cameras,this module enabling the following steps to be performed: A first step210 periodically stores the pixels in the pairs of images of the forwardfield of vision Va of the real three-dimensional road 110 (FIG. 2)generated by the stereoscopic system 60 (FIGS. 1 and 2). An imageprocessing step 220 stores the pixels of the reference road 100 and therelative values of the profile of the real road 110 in relation to thelinear profile of the reference road 100 (FIG. 2).

In parallel to this, a step 230 acquiring and storing successive valuesof the six basic rotational and translational positional parameters ofthe path of the camera Ts is also performed using the images saved instep 210.

The values of the six basic positional parameters in step 230 and therelative values of the profile of the real three-dimensional road 110 inrelation to the linear profile of the reference road 100 (step 220) areused to determine the path Ts of the vehicle (FIG. 3) using successivevalues of the specific positional parameters, knowing the speed of thevehicle (step 235). In the example embodiment, the specific positionalparameters are the height “h” of the irregularities 101 in the realthree-dimensional road 110 on which the vehicle is moving, as well asthe height “z” and pitch rotation “ε” of the vehicle (see FIG. 2).

A suspension model is selected from a model library in step 240. Themodel accurately translates the effects of the configuration of thesuspension of the vehicle being checked using the modelling type of same(distribution of equivalent springs and shock absorbers, number ofstages and control type) and the intrinsic parameter values of theseequivalents. These intrinsic parameters relate to the stiffness “K” ofthe springs and the compression ratio “C” of the shock absorbers. In theexample, the two-stage active suspension model in FIG. 2 is used. Instep 250, the mean square error ΔP² of the deviations between the valueof the intrinsic parameters of the suspension model chosen in the idealstate of same (corresponding to a new suspension system) and the valueof these intrinsic parameters corresponding to the vehicle pathparameter values stored (the specific positional parameters “h”, “z” and“⊖” in the example) are minimized. As long as the accuracy ε of thesquare error ΔP² of said deviations is less than a reference accuracyvalue ε_(R) (step 260), the previous step is repeated.

When the accuracy ε reaches a predetermined value, for example ε_(R), asuspension state diagnosis is provided as a function of the value of themean square error ΔP² (step 270). If this state corresponds to apotentially dangerous, or “pre-critical”, state, a visual alarm istriggered on the dashboard of the vehicle by sending information over acontroller area network (CAN) bus. Advantageously, if the accuracy ε isparticularly high, greater than a predetermined threshold value, it ispossible to determined a state of inflation of the tire or to identifythe suspension component (suspension members proper or tires) that isresponsible for the pre-critical state, or to predict the time of afailure.

The invention is not limited to the examples described and shown. Assuch, the invention may be applied to visual systems fitted with justone camera. The profile of the road is then detected by analyzing theoptical stream to identify movements between two successive images.

Depending on the processing power available, the suspension modelselected may be more or less sophisticated and the number of basicpositional and suspension parameters may be adjusted to advantageouslyobtain adequate accuracy, that is greater than a predetermined thresholdvalue, corresponding to the desired information on suspension andpotentially inflation state.

Furthermore, the noise in the disparities between pairs of images in astereoscopic visual system is advantageously filtered, in particular byapplying mathematical morphology tools to a disparity map.

1. A method for checking the state of degradation of a suspension system(10) fitted to a motor vehicle (1) comprising the following steps:periodic acquisition (step 210) of successive images of a forward fieldof vision (Va) provided by at least one camera (6, 7) in a visual system(60) carried on board the vehicle (1) and stored in the form of pixels(step 210), storage of positional data (step 220) of a three-dimensionalroad (110) in relation to a reference road (100) considered to be flat,using the pixels stored in the previous step (step 220), storage of thebasic rotational and translational positional parameter data (step 230)of a path (Ts) of the vehicle (1) using the positional data memorized inrelation to the reference road (100) (step 230), minimization of anerror (ΔP²) (step 250) between the predetermined intrinsic suspensionparameter values (K, C) of a suspension model in an ideal state and theintrinsic suspension parameter values of said model corresponding to thebasic positional parameter data of the path (Ts) stored in the previoussteps (220, 230) (step 250), iteration of the previous step (step 260)until an accuracy ε of said error (ΔP²) reaches a predetermined valueε_(R) to diagnose a state of the suspension (270) as a function of theerror (εP²) determined during the previous step (step 260), andtriggering of an alarm in the event of diagnosis (step 270) of apre-critical suspension state.
 2. The method for checking the state of asuspension system as claimed in claim 1, wherein, the on-board visualsystem is a stereoscopic system (60) comprising two cameras (6, 7)providing pairs of images in order to generate three-dimensional data onthe basis of the disparities between each pair of images.
 3. The methodfor checking the state of a suspension system as claimed in claim 2,wherein a noise of the disparities is filtered digitally.
 4. The methodfor checking the state of a suspension system as claimed in claim 1,wherein the reference road (100) considered to be flat is determined byaveraging the standard deviations of the positional data of the realthree-dimensional road (110) with a predetermined number of pixels. 5.The method for checking the state of a suspension system as claimed inclaim 1, wherein the path (Ts) of the vehicle (1) is identified (235) bysuccessive values of specific parameters relating to the height (h, z)of the real three-dimensional road (110) and of the vehicle (1), and tothe roll rotation and/or pitch rotation (θ) of the vehicle (1), thesespecific positional parameter values (h, z, θ) being determined usingthe stored positional data (220, 230) for the real three-dimensionalroad (110) and the basic positional parameters.
 6. The method forchecking the state of a suspension system as claimed in claim 1, whereinthe suspension model for each wheel (5 a, 5 b) of the vehicle (1) isselected from a library (240) including a model single-stage suspensionsystem with equivalent springs (3′a, 3′b) or equivalent springs/shockabsorbers (3′a, 41, 42; 3′b, 41, 42) arranged in parallel, and atwo-stage suspension system with equivalent springs (3′a, 3′b) orequivalent springs/shock absorbers (3′a, 41, 42; 3′b, 41, 42) assembledin parallel for a suspension stage proper (11A, 11B), and withequivalent springs (5′a, 5′b) or equivalent spring/shock absorbers for atire stage (5 a, 5 b).
 7. The method for checking the state of asuspension system as claimed in claim 6, wherein the intrinsicsuspension parameters relate to the stiffness (K) of the equivalentspring or springs (3′, 5′) and the compression ratio (C) of theequivalent shock absorber or shock absorbers (41, 42) per wheel (2 a, 2b).
 8. The method for checking the state of a suspension system asclaimed in claim 1, wherein the suspension (10) is controlled usingactive, semi-active or passive control (6A, 6B).
 9. The method forchecking the state of a suspension system as claimed in claim 1, whereinthe accuracy 8 of the error (ΔP²) enables the state of inflation of thetires (5 a, 5 b) to be determined.
 10. The method for checking the stateof a suspension system as claimed in claim 9, wherein the accuracy 8 ofthe error (ΔP²) makes it possible to determine which of the suspensionproper (11A, 11B) or the tires (5 a, 5 b) is in a pre-critical state.11. The method for checking the state of a suspension system as claimedin claim 2, wherein the reference road (100) considered to be flat isdetermined by averaging the standard deviations of the positional dataof the real three-dimensional road (110) with a predetermined number ofpixels.
 12. The method for checking the state of a suspension system asclaimed in claim 3, wherein the reference road (100) considered to beflat is determined by averaging the standard deviations of thepositional data of the real three-dimensional road (110) with apredetermined number of pixels
 13. The method for checking the state ofa suspension system as claimed in claim 2, wherein the path (Ts) of thevehicle (1) is identified (235) by successive values of specificparameters relating to the height (h, z) of the real three-dimensionalroad (110) and of the vehicle (1), and to the roll rotation and/or pitchrotation (θ) of the vehicle (1), these specific positional parametervalues (h, z, θ) being determined using the stored positional data (220,230) for the real three-dimensional road (110) and the basic positionalparameters.
 14. The method for checking the state of a suspension systemas claimed in claim 3, wherein the path (Ts) of the vehicle (1) isidentified (235) by successive values of specific parameters relating tothe height (h, z) of the real three-dimensional road (110) and of thevehicle (1), and to the roll rotation and/or pitch rotation (0) of thevehicle (1), these specific positional parameter values (h, z, θ) beingdetermined using the stored positional data (220, 230) for the realthree-dimensional road (110) and the basic positional parameters. 15.The method for checking the state of a suspension system as claimed inclaim 4, wherein the path (Ts) of the vehicle (1) is identified (235) bysuccessive values of specific parameters relating to the height (h, z)of the real three-dimensional road (110) and of the vehicle (1), and tothe roll rotation and/or pitch rotation (θ) of the vehicle (1), thesespecific positional parameter values (h, z, θ) being determined usingthe stored positional data (220, 230) for the real three-dimensionalroad (110) and the basic positional parameters.
 16. The method forchecking the state of a suspension system as claimed in claim 2, whereinthe suspension model for each wheel (5 a, 5 b) of the vehicle (1) isselected from a library (240) including a model single-stage suspensionsystem with equivalent springs (3′a, 3′b) or equivalent springs/shockabsorbers (3′a, 41, 42; 3′b, 41, 42) arranged in parallel, and atwo-stage suspension system with equivalent springs (3′a, 3′b) orequivalent springs/shock absorbers (3′a, 41, 42; 3′b, 41, 42) assembledin parallel for a suspension stage proper (11A, 11B), and withequivalent springs (5′a, 5′b) or equivalent spring/shock absorbers for atire stage (5 a, 5 b).
 17. The method for checking the state of asuspension system as claimed in claim 3, wherein the suspension modelfor each wheel (5 a, 5 b) of the vehicle (1) is selected from a library(240) including a model single-stage suspension system with equivalentsprings (3′a, 3′b) or equivalent springs/shock absorbers (3′a, 41, 42;3′b, 41, 42) arranged in parallel, and a two-stage suspension systemwith equivalent springs (3′a, 3′b) or equivalent springs/shock absorbers(3′a, 41, 42; 3′b, 41, 42) assembled in parallel for a suspension stageproper (11A, 11B), and with equivalent springs (5′a, 5′b) or equivalentspring/shock absorbers for a tire stage (5 a, 5 b).
 18. The method forchecking the state of a suspension system as claimed in claim 4, whereinthe suspension model for each wheel (5 a, 5 b) of the vehicle (1) isselected from a library (240) including a model single-stage suspensionsystem with equivalent springs (3′a, 3′b) or equivalent springs/shockabsorbers (3′a, 41, 42; 3′b, 41, 42) arranged in parallel, and atwo-stage suspension system with equivalent springs (3′a, 3′b) orequivalent springs/shock absorbers (3′a, 41, 42; 3′b, 41, 42) assembledin parallel for a suspension stage proper (11A, 11B), and withequivalent springs (5′a, 5′b) or equivalent spring/shock absorbers for atire stage (5 a, 5 b).
 19. The method for checking the state of asuspension system as claimed in claim 5, wherein the suspension modelfor each wheel (5 a, 5 b) of the vehicle (1) is selected from a library(240) including a model single-stage suspension system with equivalentsprings (3′a, 3′b) or equivalent springs/shock absorbers (3′a, 41, 42;3′b, 41, 42) arranged in parallel, and a two-stage suspension systemwith equivalent springs (3′a, 3′b) or equivalent springs/shock absorbers(3′a, 41, 42; 3′b, 41, 42) assembled in parallel for a suspension stageproper (11A, 11B), and with equivalent springs (5′a, 5′b) or equivalentspring/shock absorbers for a tire stage (5 a, 5 b).
 20. The method forchecking the state of a suspension system as claimed in claim 2, whereinthe suspension (10) is controlled using active, semi-active or passivecontrol (6A, 6B).